The requirement for progressively higher magnetic disk drive storage capacities is met through the use of increased linear bit densities, increased track densities and by increasing the number of recording surfaces. The single constraint that remains unaltered is the overall size of the drive. The overall dimensions of the drive unit or the form factor is the standard that must be accommodated to make the drive a commercially acceptable product.
When two, three or four disks are used within the existing form factors, the existing head and suspension designs are adequate. As increased numbers of disks are used to achieve more disk surfaces within the same dimensions or form factor, the space between adjacent disks is reduced, making more difficult both the assembly and operation of the device. Two major problems arise, one is the height limitation and the other is the less than adequate dynamic response of existing suspension designs in the closely spaced disk environment. One way to accommodate close spacing between disk surfaces is to offset head assemblies rather than use back to back mounting so that in the side by side arrangement each head and associated suspension can utilize the full height separating adjacent disks. However, since when using a rotary actuator the object is to cause the arcuate path followed by the transducer to closely approach a chord positioned on a radius and also have the transducer axis through the transducer gap tangent to each track accessed, the use of a side by side mounting technique causes the actual paths of the transducers to deviate further from the idealized path. In addition, the use of a side by side configuration will result in a loss of storage capacity. Normally all the data surface is utilized from the outermost track at which the head will fly properly to the innermost track at which an acceptable signal can be generated at the reduced linear speed. In a side by side environment one head will not use tracks at the innermost diameter, while the other will sacrifice tracks at the outer diameter (which are the most valuable tracks). If the back to back head orientation is avoided by having the heads mounted at different radial distances from the actuator axis of rotation, a loss of storage capacity occurs since one head must operate at a much higher track density.